In a known manner, a magnetic plug is placed in a liquid circuit (typically oil, liquid coolant or fuel) inside a case containing the moving parts, such as gear wheels or bearings, that stand in said liquid.
In general, the function of the liquid circuit is to enable the lubrication and/or cooling of moving parts (typically rotating parts). It turns out that the moving parts are caused to wear away throughout their lives, for example due to the friction resulting from the contact between two toothed wheels or bearings, or rather due to the shocks or intense friction between rotating parts due to intense and abnormal vibrations propagating through the case. Whatever the cause, the wear of parts leads to the formation of particles that detach from the parts and are driven by the liquid in the liquid circuit. Insofar as the rotating parts are generally metallic, the particles resulting from the wear of parts are conductive and are generally present in the form of filings. Furthermore, the parts are most often made from a ferromagnetic type metal such as iron, i.e., a metal that is capable of being attracted by a magnetic element such as a magnet.
In a known manner, such as schematically illustrated in FIG. 1, a magnetic plug 1 comprises at one end a head or support 2 and a permanent magnet formed by a magnetic bar 3 immersed in a liquid circuit, said magnetic bar 3 attracting metallic particles 4 when the liquid circulates. The operators on site must then periodically verify the condition of these magnetic plugs, remove the particles trapped on the magnetic bar and analyze these particles, for example by analyses of the SEM Scanning Electron Microscopy and EDS Energy Dispersive Spectroscopy type. From these analyses, it is possible to identify the nature and geometry of the removed particles; depending on the removal site of the plug, one may then limit the element or elements affected by wear and take measures that will guarantee the integrity of the machine and safety of the flight. It will be noted that the magnetic plugs are most often coupled with filters, the latter used to trap non-ferromagnetic particles.
Different techniques are known that enable the operators to remove particles trapped on the magnetic plug.
A first technique consists of using adhesive tape that the operator puts in contact with the magnetic bar of the plug. Such a solution is not entirely satisfactory insofar as the particles remain stuck on the adhesive and are difficult to extract (by dissolution) for analysis. Therefore it remains a residue of particles that cannot be used in the analysis and leads to a loss of data. In addition, the adhesive may generate surface pollution of the particles that is likely to distort the material analysis results.
A second technique consists of using a cloth to remove the particles on the magnetic bar.
Such a solution also poses certain difficulties. In fact, it, is necessary to clean the cloth, by immersing it in a solvent and then filtering the product obtained to recover the particles. In addition, the use of a cloth makes the recovery of all particles difficult; consequently, all of the particles are not available to carry out the analysis and a particle residue remains present on the magnetic bar, this residue being likely to distort the indication of pollution during a subsequent control. Lastly, the use of a potentially polluted cloth may lead to a suspicion of parasite pollution.
A third technique may consist of directly removing the particles on the bar by using a magnet that is more powerful than the magnet of the magnetic bar.
However, such a solution is difficult to utilize since it would lead to a risk of altering the magnetic plug by modifying the remnant field of the latter.